Process of producing and purifying benzene carboxylic acid



United States PROCESS OF PRODUCING AND PURIFYING BENZENE CARBOXYLIC ACID Otto Grosskinsky and Bernhard Jiittner, Dortmund-living, Germany N Drawing. Application November 24, 1954 Serial No. 471,117

The present invention relates to a method of producing and purifying benzene carboxylic acids and more particularly to a method of producing benzene carboxylic acids in a reaction mass by the treatment of carboniferous material such as bituminous coals, lignites, peat and the like, or their carbonization products such as coke, tar, pitch and asphalt with nitric acid and the separation in substantially pure form of the benzene carboxylic acids from the reaction mass.

The present application is a continuation-in-part of our copending application Serial No. 244,746, filed August 31, 1951, now abandoned, for Process of Preparing and Purifying Benzene Carboxylic Acids and Esters Thereof.

It is known to prepare benzene carboxylic acids from fossilized or more recent vegetable matter or from the products and residues of carbonization obtained therefrom by oxidizing reactions carried out preferably with nitric acid, or compressed air in an alkaline medium. It is known also to combine the aforesaid oxidizing methods, subjecting for example the starting material to a preliminary oxidation process carried out by treating said material with oxidizing acids, such as nitric acid or sulfuric acid, and subsequently treating the preoxidation product so obtained with air or oxygen under superatrnospheric pressure in an aqueous alkaline medium in order to complete the oxidation. In the latter case the organic acids result as alkali salts, of course, and the free organic acids are recovered by acidifying the reaction mixture with a mineral acid and separating the organic acids from inorganic matter by extracting the reaction mixture with a suitable organic solvent.

It has been pointed out in publications that the oxidizing method carried out under superatmospheric pressure with air or oxygen in an alkaline medium results in the production of light-colored low molecular weight carboxylic acid so. that substantially only benzene carboxylic acids are obtained, whereas dark-colored higher molecular weight substances, i. e. substantially multinuclear polycarboxylic acids, are present in only nominal amounts readily removable by filtration. This is no doubt an advantage of the aforesaid alkaline oxidizing method, offering the disadvantage, however, that alkali hydroxides (NaOH, KOH, etc.) are comparatively expensive and re quire considerable amounts of mineral acid (H 80 HCl and the like) in order to set free the organic acids, the alkali hydroxides being converted thereby to worthless or almost worthless inorganic salts, such as Na SO NaCl, or the like.

The nitric acid oxidation process is considerably cheaper, the amount of HNO required being initially low and capable of being lowered still further by carrying out the process at superatmospheric pressure in the presence of gaseous oxygen, whereby the HNO is almost completely regenerated in situ. However, this nitric acid oxidizing method involves the disadvantage in that the lightcolored benzene carboxylic acids obtained are contaminated by considerable amounts of dark-colored high-molecular Weight polycarboxylic acids, the oxidation product atent O Patented Jan. 7, 1958 thus comprising a dark-brown colored mass. In accordance with a known prior art process this intermediary product is purified by mixing the crude reaction product with sulfuric acid, heating the mixture and subsequently distilling off the benzene carboxylic acids. This process, however, shows the disadvantage of resulting only in pretty moderate yields, since a good deal of the lightcolored acids is decomposed by the aforesaid rigid sulfuric acid treatment.

Consequently, applicants have developed a novel and economical process of producing benzene carboxylic acids in considerably higher yields by treating the dark-colored oxidation product produced by the nitric acid oxidation of carboniferous material in a novel and dilferent manner with sulfuric acid, saving time and, moreover, chemical agents.

It is accordingly an object of the present invention to provide a novel method of obtaining substantially pure benzene carboxylic acids in an economical manner and in very high yield.

It is another object of the present invention to provide a method of producing benzene carboxylic acids from carboniferous material by initially oxidizing the carboniferous material with nitric acid, whereby the economical disadvantages in the production of benzene carboxylic acids by nitric acid oxidation are avoided.

Still another object is the development of a novel process of oxidizing carboniferous material in the production of a high yield of substantially pure benzene carboxylic acids.

Other objects and advantages will be apparent from the following description.

With the above objects in view, the present invention mainly consists in a process of producing benzene carboxylic acids from the oxidation products of a carboniferous material obtained by the oxidation of said carboniferous material with nitric acid, the process comprising the steps of mixing the oxidation products with sulfuric acid, heating the thus formed mixture at a temperature below the boiling point of the sulfuric acid so as to increase the amount of benzene carboxylic acids contained in the mixture, cooling the thus formed reaction mass, diluting the cooled reaction mass with water, extracting the benzene carboxylic acids from the dilute, cooled reaction mass by means of an organic solvent for the benzene carboxylic acids, and recovering a mixture of substantially pure benzene carboxylic acids.

It has been now discovered that a high yield of benzene carboxylic acids can be obtained in an essentially simpler and cheaper way by heating the aforesaid dark-colored oxidation product, obtained by the nitric acid oxidation of carboniferous material, with sulfuric acid at a lower temperature, namely, below the boiling point of the sulfuric acid, and subsequently separating the benzene carboxylic acids in any suitable manner, such as by extracting, but not by distillation. Since this process necessitates small amounts of sulfuric acid, expenses are low. Furthermore, the process requires only a short period of time, thereby afiording another economy in the production of benzene carboxylic acids. The heating temperature and the quantity of sulfuric acid used is dependent on the nature of the oxidation products. More specifically, if the oxidation of these products is far advanced, a smaller amount of sulfuric acid. is employed and the temperature maintained lower accordingly. Most preferably, the amount of sulfuric acid used is approximately equal in weight to the Weight of the oxidation product.

The mixture of benzene carboxylic acids obtained by oxidation and separation according to the above description, are suitably purified by recrystallizing in nitric acid. The mother-liquids obtained thereby are enriched with high molecular nitrogemcontaining impurities. Consequently, it is desirable to. evaporate these mother-liquors to obtain as dry a residue as possible, and treat this dry residue again with sulfuric acid, as described above, whereby additional amounts of benzene carboxylic acids are obtained, these acids being isolated in the manner pointed out above. The lower molecular nitrogen-containing compounds may be separated, prior to the sulfuric acid treatment, by extraction with solvents, such as benzene, ethylene trichloride and the like.

Any suitable solvent may be used for the extraction of the benzene carboxylic acids from the cooled reaction mass obtained from the sulfuric acid treatment of the nitric acid oxidation products of the carboniferous material. Ether for example has proved to be highly suitable for this purpose. Alcohols such as butyl alcohol, allyl alcohol and the like are also suitable for this purpose. The use of an alkcohol such as butyl alcohol is further advantageous in that it is possible thereby to directly esterify the benzene carboxylic acids with the alcohol used for the extraction. The thus formed esters have proved to be very valuable commercial products.

The mixture of benzene carboxylic acids or the mixture of esters obtainable therefrom are excellent starting materials for the manufacture of various commercial products, such as lacquers, films, plasticizers and the like. Furthermore, mixtures of acid esters of the kind in question have proved to be effective remedies against skindiseases (eczema) caused by pathogenic fungi, such as athletes foot. Such remedies are prepared by esterifying the benzene carboxylic acid with mom-alcohols, which may be either aliphatic or aromatic Unsaturated alcohols containing not more than 3-8 carbon atoms in the molecule are especially useful.

The following examples are additionally illustrative of the present invention but are not be conconstrued as limiting the scope thereof. All parts are given by weight.

Example I 100 parts of a dark-colored oxidation product with a permanganate number of 490, obtained by oxidizing a bituminous coal with nitric acid, are mixed with 200 parts of sulfuric acid (sp. gr. 1.84) and heated slowly to a temperature of 195 C. (measured in the mixture). Subsequently the heating is stopped whereby the temperature still rises to 209 C. After cooling, the residue is diluted with water, and subsequently the benzene car boxylic acids are extracted with ether. As crystallization product 32 parts of a mixture of benzene carboxylic acids are obtained by recrystallization from dilute nitric acid, whereas about 33 further parts, contaminated by nitrogenous products, remain in the filtrate. After evapo rating the filtrate, drying the residue, and treating said residue once more with sulfuric acid, 19 additional parts of a mixture of pure benzene carboxylic acids are obtained.

Example II 100 parts of a raw product obtained by pressure oxidation of a gas coal with nitric acid, are extracted exhaustively with benzene from acid solution. As by-prodnet 16 parts of a mixture of nitrogenous compounds are obtained. 84 parts of a purified raw product with a permanganate number of 320 remain. These are mixed with 84 parts of sulfuric acid and heated to 170 C.,'no exothermic reaction ensuing herein. After diluting with water, extracting, and crystallizing, according to Example I, 54 parts of a mixture of benzene carboxylic acids are obtained.

Example III 100 parts of a raw product obtained by pressure oxidation of a bituminous coal (with 36% volatile matter) with nitric acid, showing a permanganate number of 220, are heated after mixing with 100 parts of sulfuric acid for minutes at 155 C. (measured in the mixture). After diluting with water, butyl alcohol is added and the whole heated for a short time. The benzene carboxylic acids are quickly absorbed in the alcohol, whereafter the aqueous sulfuric acid phase is separated and the benzene carboxylic acids are esterified with the butyl alcohol. 82 parts of a mixture of esters are obtained. By distillation in vacuo (1 mm.) 62 parts of a mixture of esters with a boiling range between 220 and 270 C. are obtained.

Example IV 1.00 parts of a raw product obtained from a low temperature coke by pressure oxidation with nitric acid are heated to 180 C. for one hour with parts of sulfuric acid. After cooling, 700 parts of nitric acid (sp. gr. 1.3) are added and the mixture boiled for a short period of time. The product is evaporated to about one third of its original volume, then allowed to cool and crystallize. The separated crystals consist of 40 parts of a mixture of benzene carboxylic acids. The filtrate may be evaporated and the residue, as shown in Example I, treated once more with sulfuric acid.

Example V parts of a raw product obtained by oxidation of high temperature tar-pitch with nitric acid are heated to 190 C. for 30 minutes with 250 parts of sulfuric acid. After working up, according to Example I, 5 8 parts of of a mixture of benzene carboxylic acids are obtained.

Example VI 100 parts of an oxidation product obtained by pressure oxidation of a coking coal with nitric acid are mixed with 200 parts of sulfuric acid (sp. gr. 1.84), slowly heated to 250 C., and kept at this temperature for 5 hours. After cooling, diluting with water, and extracting with ether, the ether is distilled off carefully, and the residue crystallized from dilute nitric acid. 35 parts of benzene carboxylic acids are obtained. After evaporating the nitric acid filtrate and again treating the residue with sulfuric acid, 17 additional parts of benzene carboxylic acids are obtained. The acids (52 parts) are combined and esterified with allyl alcohol to an acid number of 80. The esters so obtained are very active against skin disease such as athletes foot.

While the invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications may be made and equivalents substituted therefor without departing from the principles and true nature of the present invention.

What is claimed by Letters Patent is:

1. A process of producing benzene carboxylic acids from the oxidation products of a carboniferous material selected from the group consisting of bituminous coals, lignites, peat and carbonization products thereof obtained by the oxidation of said carboniferous material with nitric acid to form a reaction mixture including said oxidation products, said process comprising the steps of separating said oxidation products from the remainder of said reaction mixture; mixing said oxidation products with sulfuric acid; heating the thus formed mixture at a temperature of from C. to below the boiling point of the sulfuric acid so as to increase the amount of benzene carboxylic acids contained in said mixture; cooling the thus formed reaction mass; diluting said cooled reaction mass with water; extracting said benzene carboxylic acids from said diluted, cooled reaction mass by means of an organic solvent for said benzene carboxylic acids; and recovering a mixture of substantially pure benzene carboxylic acids.

2. A process of producing benzene carboxylic acids from the oxidation products of a Carboniferous material selected from the group consisting of bituminous coals, lignites, peat and carbonization products thereof obtained by the oxidation of said carboniferous material with nitric acid to form a reaction mixture including said oxidation products, said process comprising the steps of separating said oxidation products from the remainder of said reaction mixture; mixing said oxidation products with an amount of sulfuric acid approximately equal in weight to the weight of said oxidation products; heating the thus formed mixture at a temperature of from 155 C. to below the boiling point of the sulfuric acid so as to increase the amount of benzene carboxylic acids contained in said mixture; cooling the thus formed reaction mass; diluting said cooled re action mass with water; extracting said benzene carboxylic acids from said diluted, cooled reaction mass by means of an organic solvent for said benzene carboxylic acids; and recovering a mixture of substantially pure benzene carboxylic acids.

3. A process of producing benzene carboxylic acids from the oxidation products of a carboniferous material selected from the group consisting of bituminous coals, lignites, peat and carbonization products thereof obtained by the oxidation of said carboniferous material with nitric acid to form a reaction mixture including said oxidation products, said process comprising the steps of separating said oxidation products from the remainder of said re action mixture; mixing said oxidation products with sulfuric acid; heating the thus formed mixture at a temperature of from 155 C. to below the boiling point of the sulfuric acid so as to increase the amount of benzene carboxylic acids contained in said mixture; extracting said benzene carboxylic acid from said reaction mass by means of an organic solvent for said benzene carboxylic acids; and recovering a mixture of substantially pure benzene carboxylic acids.

4. A process of producing benzene carboxylic acids from the oxidation products of a carboniferous material selected from the group consisting of bituminous coals, lignites, peat and carbonization products thereof obtained by the oxidation of said carboniferous material with nitric acid to form a reaction mixture including said oxidation products, said process comprising the steps of separating said oxidation products from the remainder of said reaction mixture; mixing said oxidation products with sulfuric acid; heating the thus formed mixture at a temperature of from 15 C. to below the boiling point of the sulfuric acid so as to increase the amount of benzene carboxylic acids contained in said mixture; cooling; the thus formed reaction mass; diluting said cooled reaction mass with water; extracting said benzene carboxylic acids from said diluted, cooled reaction mass by means of an organic solvent for said benzene carboxylic acids; evaporating said organic solvent from the thus formed solution; recrystallizing the residue from said evaporation in dilute nitric acid; and recovering a mixture of substantially pure beli zene carboxylic acids.

5. A process of producing benzene carboxylic acids from the oxidation products of a carboniferous material selected from the group consisting of bituminous coals, lignites, peat and carbonization products thereof obtained by the oxidation of said carboniferous material with nitric acid to form a reaction mixture including said oxidation products, said process comprising the steps of separating said oxidation products from the remainder of said reaction mixture; mixing said oxidation products with sulfuric acid; heating the thus formed mixture at a temperature of from C. to below the boiling point of the sulfuric acid so as to increase the amount of benzene carboxylic acids contained in said mixture; cooling the thus formed reaction mass; diluting said cooled reaction mass with Water; extracting said benzene carboxylic acids from said diluted, cooled reaction mass by means of an organic solvent for said benzene carboxylic acids; evaporating said organic solvent from the thus formed solution; heating the thus obtained residue with sulfuric acid at a temperature of from 155 C. to below the boiling point of the suliuric acid; cooling the thus formed reaction mass; diluting said cooled reaction mass with water; extracting the benzene carboxylic acids from the thus formed reaction mass by means of an organic solvent for said benzene carboxylic acids; and recovering a mixture of substantially pure benzene carboxylic acids.

References Cited in the file of this patent UNITED STATES PATENTS 2,193,337 Leicester Mar. 12, 1940 2,461,740 Kiebler Feb. 15, 1949 2,555,410 Howard June 5, 1951 2,673,216 Goedkoop Mar. 23, 1954 2,726,262 Grosskinsky et a1. Dec. 6, 1955 2,762,840 Howard Sept. 11, 1956 FOREIGN PATENTS 149,974 Great Britain Nov. 3, 1921 635,088 Great Britain Apr. 5, 1950 652,935 Great Britain May 2, 1951 OTHER REFERENCES Franke et al.: Chemical Industries, 58, pp. 580-581 1946). 

1. A PROCESS OF PRODUCING BENZENE CARBOXYLIC ACIDS FROM THE OXIDATION PRODUCTS OF A CARBONIFEROUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF BITUMINOUS COALS, LIGNITES, PEAT AND CARBONIZATION PRODUCTS THEREOF OBTAINED BY THE OXIDATION OF SAID CARBONIFEROUS MATERIAL WITH NITRIC ACID TO FORM A REACTION MIXTURE INCLUDING SAID OXIDATION PRODUCTS, SAID PROCESS COMPRISING THE STEPS OF SEPARATING SAID OXIDATION PRODUCTS FROM THE REMAINDER OF SAID REACTION MIXTURE; MIXING SAID OXIDATION PRODUCTS WITH SULFURIC ACID; HEATING THE THUS FORMED MIXTURE AT A TEMPERATURE OF FROM 155*C. TO BELOW THE BOILING POINT OF THE SULFURIC ACID SO AS TO INCREASE THE AMOUNT OF BENZENE CARBOXYLIC ACID CONTAINED IN SAID MIXTURE; COOLING THE THUS FORMED REACTION MASS; DILUTING SAID COOLED REACTION MASS WITH WATER; EXTRACTING SAID BENZENE CARBOXYLIC ACIDS FROM SAID DILUTED, COOLED REACTION MASS BY MEANS OF AN ORGANIC SOLVENT FOR SAID BENZENE CARBOXYLIC ACIDS; AND RECOVERING A MIXTURE OF SUBSTANTIALLY PURE BENZENE CARBOXYLIC ACIDS. 